Synopsis This work sums up to how voluntary arbitration is embedded in administrative law and how it was constituted in the tax law. It seeks to answer the question below: should the model of arbitration in tax matters follow the example of the administrative model? Arbitration, whose origin is ancient, is a jurisdictional means of resolving lawsuits. Nowadays it defines itself as an institution re-emerging with all its strength. Arbitration has many forms and is may be voluntary or required, ad hoc or institutional, by law or according to equity, domestic or international affairs. The arbitrary courts have a mixed nature. Several obstacles have been overcome, in common with the Administrative Law and with the Tax Law and specific to both branches of public law. Nevertheless, the arbitrability of the lawsuits doesn´t assume itself as a general principle of arbitrability in both branches of the judicial science in study. Whether in administrative or in tax matters, arbitration is restricted to certain issues. The regimes established in both branches of law differ. In fact, the system of arbitration in administrative matters is limited practically to refer to the Voluntary Arbitration Law. On the contrary, the model set out in Tax Law presents a more densified arbitrary regime and specially created for the field of taxation. Nevertheless, the valuable contribution of the broad acceptance of arbitration should not be ignored in the reform of the governmental office for litigious matters (2002/2004), for an emergency of debate in what concerns the arbitration among the doctrine related to Tax Law. There are several aspects to the administrative model which could be followed by the legislature (some of which already were) in shaping the regime of arbitration in what concerns tax matters. Other aspects, negative in our pion-of-view, are recommended to be removed from the tax code. However, it seems that legislator in the Taw Law was very cautious, leading us to question the possibility of a new researched paper with the reversed question, which is the following: Arbitration in administrative matters: in conformity with the tax model?